Cleanup Python sys.path setup in ParaView.

Cleaning up the logic to setup Python sys.path for build and install locations
for all supported platforms. This refactoring makes it easier to update and
correct paths, if needed, in future versions.

Change-Id: I4d818331d0cfb3c07e823c26dc95054adbaa89f0
Merge topic 'fix_python_paths' into next

3eed8f6 Cleanup Python sys.path setup in ParaView.